The present invention relates to veneer lathes, and particularly to a stabilizer and a method for its use for helping to hold a log of wood properly aligned with the spindles of a veneer lathe during cutting of veneer from the log.
Veneer for use in manufacture of plywood is commonly produced on a veneer lathe by cutting ("peeling") a thin spiral layer from a log. As transportation and energy costs increase and the cost of timber suitable for use in veneer also increases, the economic justification of maximizing the yield and quality of veneer from every log becomes more apparent.
In the usual lathe used for production of veneer for plywood, a log, normally called a "block," is held horizontal and rotated about a central longitudinal axis, while a veneer knife having an upwardly exposed edge extending parallel with the block's axis of rotation is moved toward the center of the block at a regular rate. Normally, a pressure bar, such as a roller nose bar, extends parallel with the edge of the veneer knife and is located a predetermined distance above and radially outward from the edge. The pressure bar provides pressure against the block which helps to govern the thickness of the veneer peeled, and which determines to some extent whether the veneer splits or is solid.
Economical production of high quality veneer requires close control over the position of a block being peeled, as well as accurate control of the movement and position of the veneer knife of the lathe during peeling. Since the nominal thickness of much veneer cut for manufacture of plywood is 1/10 inch, a variation in veneer thickness of only 0.001 inch is a change in yield of 1%.
It has been customary in the past to control the position of a block being peeled by the chucks and pressure bar of the lathe, until the block being peeled has become so small that flexure becomes a possible problem. Flexure of a block being peeled often results in veneer which is not flat and is therefore unsatisfactory for manufacture of plywood. The veneer may cup toward its center and split at the lateral edges if the block bows away from the knife and veneer is cut thinner in the middle than at the ends of the block.
Core bracers have been used in the past to try to keep veneer flat by preventing such flexure of the middle portion of a block being peeled. Such core bracers previously used include short rollers which contact only a middle portion of the length of the block. If such a prior art core bracer bends the block toward the veneer knife, however, it may result in the block becoming too slender in the center, creating veneer having wavy edges.
Additionally, flexure of the spindles of veneer lathes allows some variation of veneer thickness as the entire block moves relative to the veneer knife. In order to assure veneer of at least the minimum thickness, it has previously been necessary to cut veneer slightly thicker than actually desired. This, too, reduces the yield from each block.
Prior art core bracers have typically attempted to keep the center portion of a block aligned with the ends of the block where the chucks support it by using a tracer to follow the surface of the block near an end. A problem frequently encountered in use of such core bracers is that surface irregularities apparent at the end of a block are proliferated and perpetuated, rather than being eliminated, and the quality of veneer produced is not as good as is desired.
Some types of core bracers utilized in the past interfere with the use of automatic veneer lathe chargers which automatically place blocks into the chucks of a veneer lathe in the position which is calculated to produce the greatest amount of veneer from each block. Other previously known core bracers and similar devices can not be precisely positioned in correlation with the intended location of the block being peeled. For instance, many core bracers include parallel rollers on a pivoted head which provides some support, yet still permits a significant amount of movement of the veneer block. Yet other core bracers, when in use, obstruct the lathe operator's view of the peeling operation.
Veneer blocks often contain imperfections, such as radial cracks (checks) and annular cracks (pitch rings). Either of these may result in a block splitting apart before it has been peeled to the desired minimum diameter. A lathe operator, observing the presence of a pitch ring or a large radial check, usually prefers to drop such block from the chucks of the lathe, before it can split apart, possibly plugging or damaging the lathe. It would be desirable, however, to produce a maximum amount of veneer from such portions of a veneer block which might otherwise be ejected from the lathe by the lathe operator.
As a block is peeled from an original large diameter to a smaller diameter the upward force exerted by the knife during cutting of veneer at a particular surface speed remains approximately constant as the weight of the block being peeled decreases. As a result, the block tends to rise slightly with respect to the edge of the knife, changing the effective angle between the knife and the surface of the block. The tendency of the block to rise changes the angle of incidence of the knife relative to the surface of the block and thus tends to change the thickness of the veneer produced.
What is needed, therefore, is apparatus and a method for its use to provide improved control of the thickness of veneer produced and to enhance production of a greater amount of veneer from a given block through stabilization of the location of the block throughout the process of peeling. Such a device and method should be usable in conjunction with a veneer lathe equipped with an automatic log charger, without interfering with use of the charger.